Electrostatic dust collector

ABSTRACT

An apparatus for separating particulate matter from a gas stream wherein dirty gas is moved through an electrostatic precipitator to remove most of the particulate matter and then is moved through a filter of foraminous material while an electric field is applied to the filter whereby the remainder of the particulate matter is removed. The precipitator is generally cylindrical wherein the gas flows axially therein and then radially outwardly from the precipitator, and the foraminous filter is generally tubular and surrounds the precipitator in spaced relation. A tubular screen or grid connected to a suitable electrical potential and positioned adjacent the filter is utilized for applying an electric field to the filter.

United States Patent [1 1 Reed et al.

[ Oct. 28, 1975 ELECTROSTATIC DUST COLLECTOR [73] Assignee: American Precision Industries Inc.,

Buffalo, NY.

[22] Filed: Nov. 24, 1972 [21] Appl. No.: 309,074

[52] US. Cl. 55/112; 55/124; 55/131; 55/137; 55/147; 55/154; 55/304; 55/379;

55/432; 55/DIG. 38

[51] Int. Cl. B03C 3/06 [58] Field of Search 55/2, 6, l2, 13, 101, 108, 55/112, 124, 128, 131, 133, 136, 137,138, 139,140,141, 142, 146, 147, 148, 149, 150,

151, 154, 155, DIG. 38, 304, 379, 432

[56] References Cited UNITED STATES PATENTS 895,729 8/1908 Cottrell 55/151 X 1,790,961 2/1931 Welch 55/128 1,931,436 10/1933 Deutsch.. 55/152 X 2,004,352 6/1935 Simon I 310/ 2,058,732 /1936 Simon I 250/495 X 2,397,197 3/1946 Newman /473 X 2,462,890 3/1949 Newman 55/105 2,502,560 4/1950 Dahlman 55/132 2,556,982 6/1951 Roos et a1 55/131 2,634,818 4/1953 Wintermute 55/139 X 2,776,724 1/1957 Goldschmied 55/138 2,805,732 9/1957 Martinez 55/430 X 3,365,858 l/l968 Penney 55/11 3,577,705 5/1971 Sharlit 55/300 X 3,664,092 5/1972 Vincent 55/112 3,733,784 5/1973 Anderson et a1. 55/302 FOREIGN PATENTS OR APPLICATIONS 821,900 9/1969 Canada.... 55/131 215,121 5/1958 Australia 55/131 794,038 4/1958 United Kingdom 55/154 Primary Examiner-Bernard Nozick Attorney, Agent, or Firm-Christel & Bean [5 7] ABSTRACT An apparatus for separating particulate matter from a gas stream wherein dirty gas is moved through an electrostatic precipitator to remove most of the particulate matter and then is moved through a filter of foraminous material while an electric field is applied to the filter whereby the remainder of the particulate matter is removed. The precipitator is generally cylindrical wherein the gas flows axially therein and then radially outwardly from the precipitator, and the foraminous filter is generally tubular and surrounds the precipitator in spaced relation. A tubular screen or grid connected to a suitable electrical potential and positioned adjacent the filter is utilized for applying an electric field to the filter.

+ 19 Claims, 8 Drawing Figures U.S. Patent' Oct. 28,1975 Sheet1of4 3,915,676

US. Patent Oct. 28, 1975 Sheet3of4 3,915,676

US. Patent Oct. 28, 1975 I Sheet4 of4 3,915,676

I l l l l I l l l ELECTROSTATIC DUST COLLECTOR BACKGROUND OF THE INVENTION This invention relates to the art of dust collection, and more particularly to a new and improved apparatus of the electrostatic precipitation type for separating particulate matter from a gas stream.

Dust collection methods and apparatus of the electrostatic precipitation type are well known and offer the advantage of being able to handle relatively heavy dust loads with a low pressure drop through the apparatus. A problem with electrostatic precipitators, however, is a momentary passage of dust due to arcing or similar electrical problems. Dust collection methods and apparatus of the mechanical filtration type which employ a porous filter medium, such as fabric filters or bag houses, also are well known and provide a very efficient collection of small particles with attendant safety from the risk of passage of large puffs of dust. These capabilities are limited, however, because if the filter material has small holes or is relatively porous, dust will leak or bleed through the material. This, in turn, limits the variety of filter material that can be employed and can increase the cost of construction. In addition, to achieve good results with a mechanical filter of this type, it is often necessary to collect a layer of dust on the filter medium to create a filter cake.

SUMMARY OF THE INVENTION It is therefore an object of this invention to provide a new and improved apparatus for collecting dust advantageously combining various desirable features of the electrostatic precipitation and mechanical filtration types.

It is a further object of this invention to provide such apparatus which produces results superior to those produced by either electrostatic precipitation or mechanical filtration alone.

The present invention provides apparatus for separating particulate matter from a gas stream wherein dirty gas is moved through electrostatic precipitator means to remove most of the particulate matter and then is moved through filter means of foraminous material while an electric field is applied to the filter means whereby the remainder of the particulate matter is removed. The precipitator means and filter means are positioned concentrically, and gas is caused to flow axially along the precipitator means and then radially outwardly to the filter means.

The foregoing and additional advantages and characterizing features of the present invention will become clearly apparent upon a reading of the ensuing detailed description together with the included drawing wherein:

BRIEF DESCRIPTION OF THE DRAWING FIGURES FIG. 1 is a vertical sectional elevational view of apparatus according to the present invention for separating particulate matter from a gas stream;

FIG. 2 is a plan view taken about on line 2-2 of FIG.

FIG. 3 is an enlarged sectional view taken about on line 3-3 of FIG. 1;

FIG. 4 is an enlarged fragmentary vertical sectional view, with some parts shown in elevation, of the apparatus of FIG. 1;

FIG. 5 is an enlarged fragmentary sectional view of a portion of the apparatus of FIG. 4;

FIG. 6 is an elevational view with parts broken away illustrating an installation of apparatus according to the present invention;

FIG. 7 is an elevational view looking at the right-hand side of the apparatus of FIG. 6; and

FIG. 8 is a sectional view taken about on line 88 of FIG. 6.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT Referring now to FIG. 1, the apparatus according to the present invention for separating particulate matter from a gas stream includes a housing 10 having an inlet 11 for receiving dirty gas and an outlet 12 through which cleaned gas leaves the apparatus. Housing 10 is shown in abbreviated form for convenience in illustration, and a preferred form of housing 10 will be shown in detail further on in the specification. Gas is moved through the apparatus from inlet 11 to outlet 12 by a fan 7 driven by a motor 8 and connected to outlet 12. The output of fan 7 is connected to an outlet duct 9 through which the cleaned gas is conveyed. The apparatus of the present invention further comprises electrostatic precipitator means 14 positioned within housing 10 and having an inlet communicating with dirty gas inlet 11. Precipitator 14 is disposed vertically in housing 10, is generally cylindrical in shape, and is of the type wherein gas flows in the precipitator generally axially thereof and flows out from the precipitator in a generally radial outward direction. Precipitator 14 includes a cylindrical collecting structure having an opening at one end defining the inlet of the precipitator and outlet means spaced axially from the inlet. The collecting structure comprises a cylindrical screen 18 of electrically conducting material, and an electrical line 19 is connected to screen 18 for applying an electrical potential thereto in a manner which will be described. Screen 18 is secured at one end thereof in a first, generally disc-shaped end member 20 of precipitator 14 and secured at the other end thereof in a second, generally ring-shaped end member 22 of precipitator 14, the central opening of member 22 defining the inlet for precipitator 14 as shown in FIG. 4. In preferred form, screen 18 is of stainless steel mesh with a spacing between wires of about one-half inch, and end members 20, 22 are of dielectric material such as a polyester laminate.

Precipitator 14 further comprises an elongated corona electrode 24 mounted centrally of the collecting structure. Corona electrode 24 is in the form of a relatively thin wire, preferably of stainless steel, attached at one end thereof to a connector member 24 which fits in an aperture provided in end member 20 and extends through and beyond end member 20 thereby enabling an external electrical connection to be made to wire 24. The exposed end of connector member 25 is provided with an assembly including a compression spring 26, a washer 27, and a locknut 28 for adjusting the tension on wire 24. A conductor member 29 also is connected to the end of member 25 for making an electrical connection to wire 24 in a manner which will be described. The other end of corona electrode or wire 24 is fitted through an aperture provided in a rod member 30 of dielectric material, and the tip or end of wire 24 is provided with a stop member 31 for holding it in position in rod 30. In particular, after the end of wire 24 is inserted through the aperture in rod 30, a steel button 31 is secured to the end of wire 24 by silver solder to provide a stop or retainer for abutting rod 30 to hold wire 24 in place. Opposite ends of rod 30, in turn, extend through apertures provided in a first ring member 32 secured in an annular groove provided in the outer surface of end member 22. A second ring member 33 having a diameter larger than that of ring member 32 also is secured in another annular groove provided in the outer surface of end member 22, and the annular region between ring members 32, 33 is provided with a resinous filler 34 such as catalyzed RTV-6O resin available commercially from the General Electric Company, which when cured anchors rod member 30 in place. End member 22 is provided with a peripheral surface 35 which is inclined or disposed at an angle extending in an outward direction relative to the axis of corona electrode 24. Expressed differently, surface 35 defines an obtuse angle with the lower surface of member 22 and an acute angle with the upper surface of member 22 whereby the diameter of the upper surface is slightly larger than the diameter of the lower surface. The reason for inclining the peripheral surface 35 of member 22 will be explained further on in the specification.

Screen 18 of precipitator 14 has an operative axial length substantially equal to the operative axial length of corona electrode 24 and electrode 24 is disposed preferably along the longitudinal axis of screen 18. Precipitator 14 can also include an impervious tube or sleeve 37 surrounding screen 18 in closely-spaced relation. Tube 37 is of sufficient length to extend along a major portion of the axial length of screen 18 for a purpose which will be described. Furthermore, tube 37 can be made of either an electrically conducting or a dielectric material. By way of example, an operational unit was constructed with screen 18 having a length of about 89 inches and an outer diameter of 4 7/32 inches, tube 37 having a length of about 75 inches, and wire 24 having a length of about 89 /8 inches.

The apparatus of the present invention further comprises filter means 40 of foraminous and dielectric material within housing 10 and positioned between electrostatic precipitator 14 and the clean gas outlet 12. Filter means 40 has the shape of a tube or sleeve which preferably is thin-walled, surrounds precipitator 14, and is positioned in spaced, generally coaxial relation to the collecting structure or screen 18 of precipitator 14. Filter means 40 can comprise various types of foraminous or porous dielectric material such as woven, knitted, or non-woven cloth or fabric, permeable membrane material, fibrous material, and porous plastic or other relatively rigid porous material. A type of woven cloth material found to serve satisfactorily as filter means 40 is commercially available from the DuPont Company under the designation Nomex Filter Media style N0. 1610. When filter means 40 comprises woven cloth or fabric, it has been found that filter means 40 should have a porosity or air/cloth ratio such that a gas flow of 200 cubic feet per minute through one square foot of cloth area provides a pressure drop of one-half inch of water in the apparatus. When non-woven materials are employed they should have a relatively high porosity.

The apparatus of the present invention further comprises means for applying an electric field to filter means 40. As shown in FIGS. 1 and 4, a screen or cage 45 of electrically conducting material, preferably stainless steel mesh with a spacing between wires of about one-half inch, is positioned between filter means 40 and clean gas outlet 12. Screen 45 is cylindrical in shape and surrounds filter means 40 along the entire axial length thereof. Furthermore, screen 45 is located closely adjacent filter means 40 so that the distance from precipitator 14 to filter means 40 is greater than the distance between filter means 40 and screen 45. In particular, the diameter of screen 45 is slightly larger than the diameter of filter means 40 and filter means 40 is not in close proximity to screen or cage 18 of precipitator 14. By way of example, an operational unit was constructed with filter means 40 in the form of a tube having a length of about 98 inches and an inner diameter of about 6 inches and with screen 45 having a length of about 96- inches and an outer diameter of about 7% inches. As described above, in this exemplary unit the outer diameter of screen 18 is about 4 7/32 inches. This relationship is maintained to insure proper electrical operation of the apparatus as will be described in further detail presently. An electrical line 47 is connected to screen 45 for applying an electrical potential thereto in a manner which presently will be described.

FIGS. 6-8 illustrate a preferred construction for housing 10 of the apparatus of the present invention in a typical installation. Housing 10 in the present illustration is rectangular and contains a modular arrangement including a plurality of dust collector groups or modules, in the present instance four, each of which modules in turn includes six dust collector assemblies or units. Each unit 48, of course, comprises the combination of electrostatic precipitator 14, filter means 40 and screen 45. The units are disposed vertically, and in the present instance each module contains two rows each including three units. The modules, in turn, are arranged side-by-side in a row along one vertical side wall 50 of housing 10 and between end walls 52 and 54 thereof. Each group or module is separated from an adjacent module by a corresponding one of a plurality of spaced vertical partition walls 55. The other side wall 56 of housing 10 is spaced from the dust collector modules and is provided with inlet 1 1 for receiving dirty gas and outlet 12 through which cleaned gas leaves the ap' paratus.

The dust collector units are supported within housing 10 in the following manner. A base or supporting member 60 is secured or otherwise fixed within housing 10 near but spaced from the bottom thereof. Supporting member 60 extends along the entire length of housing 10 between end walls 52 and 54 and thereby supports all of the dust collector units comprising the plurality of modules thereof. Supporting member 60 is provided with an opening or aperture for each of the dust collector units through which aperture the incoming dirty gas enters the electrostatic precipitator 14 of the corresponding unit. As shown in FIG. 4, each aperture 62 is surrounded by a supporting and sealing structure comprising a first ring member 63 having a diameter slightly larger than that of aperture 62 and secured such as by tack welding to member 60 and a second ring member 64 surrounding ring 63 in concentric relation therewith and having an axial length or height greater than that of ring 63. Ring 64 also is secured such as by tack welding to member 60 and is formed with a groove 66 in the outer surface thereof for a purpose to be described. Accordingly, in this illustrative arrangement including four modules each containing six dust collector units for a total of 24 units, supporting member 60 is provided with 24 apertures 62 and 24 corresponding arrangements of rings 63 and 64.

Each dust collector unit is supported at the bottom thereof on member 60 in the following manner. Screen 45 of each unit has an inner diameter larger than the outer diameter of ring 64 and the unit is placed over its corresponding aperture 62 with screen 45 resting on member 60 and surrounding ring 66. Screen or cage 45 has sufficient rigidty to support the entire unit in a manner which will be described. The tubular filter means 40 fits relatively closely onto ring member 64 and a clamping ring is fitted onto filter 40 tightly over groove 66 in ring 64 whereby a substantially air-tight seal is provided between the end of tubular filter means 40 and ring 64. The inner ring member 63 penetrates a short distance into filler 34 between ring members 32, 33 whereby the central opening of insulator member 22 is in fluid communication with aperture 62 for receiving an incoming flow of dirty gas and a substantially fluid-tight seal is provided between ring member 63 and filler material 34. Furthermore, the bottom of precipitator 14 including insulator member 22 is supported by ring member 63. Accordingly, each dust collector unit is supported at the bottom thereof by a corresponding portion of the supporting member 60.

Each dust collector unit includes a tensioning means designated 80 supported by screen 45 and connected to filter means 40 near the top thereof as viewed in FIG. 4. Filter means 40 is provided with means in the form of a bead 82 adjacent the bottom end thereof as viewed in FIG. 4 for engaging precipitator 14 near the bottom end whereby the tension applied to filter 40 is applied also to precipitator 14. The apparatus also includes means in the form of a tube or sleeve 84 secured at one end to insulator member and fixed at the other end thereof for limiting or preventing movement of precipitator 14 as tension is applied thereto. The tension applying means 80 comprises a closure cap member 86 having a generally planar body portion 87 and an annular flange 88 depending therefrom. Cap member 86 rests on and is supported by the rigid screen or cage 45 and comprises the top of each dust collector unit. A connecting member 89 in the form of a ring having an outer diameter less than the inner diameter of flange 88 and having two annular flange portions defining a right angle therebetween connects filter means 40 to cap member 86. The top or upper end of filter means 40 is secured to connecting member 89 by a clamp member 90, and member 89, in turn, is secured to body portion 87 of cap member 86 by suitable fastening means designated 92. A second connecting member 94 having a shape similar to that of member 89 is positioned within filter 40 a short distance from the top thereof and is secured thereto by means of a clamp 96. Member 94 is supported by means of a bolt 97 extending through connecting members 94 and 89 and through cap 86, and the end of bolt 97 projecting outward beyond cap 86 is provided with a compression spring 99, washer 100 and nut 101. Additional supporting means, for example three, each including a bolt,

compression spring, washer and nut are positioned around the circumference of the assembly as shown in FIG. 2. As a result, spring 99 applies a tension force to fabric filter 40 urging it in a direction toward closure cap member 86. The tension is adjustable externally of the assembly merely by rotating nut 101 to adjust the compression of spring 99. As filter means 40 is pulled taut toward cap 86, the engagement between bead 82 and inclined surface 35 of insulator 22 tends to pull precipitator l4 upwardly as viewed in FIG. 4, and upward movement thereof is limited or constrained by tube 84 which is fixed between insulator 20 and cap 86.

Bead 82 adjacent the other end of fabric filter 40 can be provided by securing a hoop or wire ring 103 to the inner surface of filter 40 by enclosing the ring within a folded strip of cloth 104 and then sewing strip 104 to the inner surface of filter 40 as illustrated in FIG. 5. The bead provides a wedge-like member which fits snugly against peripheral surface 35 of member 22 when filter means 40 is pulled taut. This, in turn, transmits tension force to the precipitator assembly 14 and provides a substantially fluid-tight seal between filter 40 and insulator member 22 to prevent escape of gas from the region therein. Sleeve 84 is of a diameter enabling it to be fitted within filter 40 as well as within connector members 89 and 94. Tube 84 is of a length so as to fit snugly between insulator member 20, actually being slightly embedded therein, and closure cap member 86. A corresponding tension applying arrangement is provided on each of the dust collector units in the installation of FIGS. 6-8.

Each closure cap member 86 is provided with a central hollow boss or extension 105 enabling each unit to be mechanically connected to a vibrator means 108 as shown in FIG. 6 for shaking the units whenever they are to be cleaned. In particular, vibrator 108 is of the compressed air operated type and functions to impart generally horizontal vibratory movement to each of the dust collector units by a connecting rod or member 109 extending from vibrator 108 and received in the boss or extension 105 of each closure cap member 86. A supply line 110 connects vibrator 108 to a source of compressed air (not shown). A single vibrator member 108 is provided for each module of six units thereby requiring four vibrator assemblies 108 to be included in the installation of FIGS. 6-8. As a result, the six dust collector units in each module can be vibrated simultaneously.

The apparatus of the present invention further comprises means for controlling the flow of gas through the dust collector units, and in particular for stopping the flow of gas from a unit to the clean gas outlet 12 when that dust collector unit is being vibrated to remove collected dust therefrom. According to a preferred mode of the present invention, the flow of gas through the several dust collector units of each group or module is controlled by a single arrangement, the control of the several modules in turn, being performed separately or independently. Referring first to FIG. 6, the spacedapart vertical partitions 55 meet an assembly which provides a passage or chamber connecting each module with the common outlet 12. The assembly includes a vertical wall extending parallel to but spaced from housing sidewall 56 which wall joins edges of partitions 55. A first horizontal wall 116 joins wall 115 to housing sidewall 56 below outlet 12, and as a result a chamber or passage connecting outlet 12 to all of the modules is defined by sidewall 56, vertical wall 1 15 and horizontal wall 116. A second horizontal wall 117 joins wall 115 with housing sidewall 56 above inlet 11 and below outlet 12 thereby providing a common passage or chamber between inlet 11 and the inlets of the dust collector units.

Each group or module of dust collector units normally is in fluid communication with outlet 12 thereby allowing flow of cleaned gas from the dust collectors to outlet 12. Fluid communication is selectively and independently blocked or shut-off between each group or module and outlet 12 by damper means provided for each group or module. Referring now to FIGs. 6 and 7, each module is provided with a damper member 120 disposed generally horizontally and moved vertically by means of a pneumatic cylinder 122 mounted at the top of housing having a piston rod 123 connected to damper member 120. Movement of damper member 120 in an upward direction can be limited by suitable stop members (not shown) secured to and extending downwardly from the top wall of housing 10. Movement of damper member 120 in a downward direction is limited by upstanding generally vertical flange members 126, 127 provided on wall members 56, 115 and on partitions 55. In other words, an arrangement of flange members 126, 127 is included for each module of dust collector units which flange members define a rectangular opening connecting the particular module with the common passage to outlet 12. When the corresponding damper members 120 is lowered so as to be seated on the top edge of flange members 126, 127 the corresponding module is closed thereby preventing any further gas flow from that particular module of dust collectors to outlet 12.

The bottom of housing 10 includes tapered sidewalls 130, 132 thereby defining a hopper into which collected particulate matter such as dust falls when the dust collector units are vibrated. Removal of dust from the hopper is facilitated by provision of a screw conveyor therein (not shown) driven by a motor 134 mounted on the housing 10 and connected to the conveyor through a suitable coupling 135, for conveying the particulate matter to one end of the hopper. An outlet is provided in the hopper bottom at that end and is closed by a Razzer type valve 137 which provides a bladder type or vacuum seal for the outlet. In other words, the hopper outlet normally is closed by valve 137 until the weight of accumulated dust is sufficient to force valve 137 open to allow emptying of the hopper into a suitable receptacle for transporting the dust away from the installation. A power supply generally designated 138 is located at the bottom of the installation and can be one of several commercially available electrostatic precipitator power supplies which provide a maximum voltage output of about 50,000 volts.

The apparatus of the present invention operates in the following manner. The operation of a single unit as shown in FIGS. l5 will be described, it being understood that the same operation occurs for each unit in a multiple unit installation as shown in FIGS. 6-8. Referring now to FIGS. 1 and 4, dirty gas is introduced to the apparatus through inlet 11 and is moved by operation of fan 7 through electrostatic precipitator means 14 to collect a major portion of the particulate matter from the gas stream. In particular, the gas to be cleaned flows through aperture 62 of plate 60 into the precipitator 14 at the bottom thereof as viewed in FIG. l, and flows axially within precipitator 14 along the length of tube 37 whereupon the gas flows outwardly in a generally radial direction through screen 18. In the present instance corona wire or electrode 24 is maintained at a relatively negative potential, i.e. ground, and screen 18 is connected to a relatively positive potential. Therefore, conductor 19 is connected to the positive terminal of the power supply, such as power supply 138 in the installation of FIGS. 6-8, and conductor 29 shown in FIG. 4 is connected to housing 10. The magnitude of the electrical potential applied will vary depending upon the overall dimension of the dust collector units, and for a typical unit wherein screen 18 has a diameter of about 4 inches, the potential difference typically would be about 30,000 volts. Furthermore, the relative polarities of corona electrode 24 and screen 18 can be changed. Having corona electrode 24 at a relatively negative potential is preferred because it has been found to provide a more stable corona at a relatively larger current to provide more efficient dust collection.

The portion of the apparatus comprising corona electrode 24, tube 37 and screen 18 is essentially a tubular, coaxial electrostatic precipitator. Dust particles and other particulate matter entering this portion of the apparatus are charged in the corona current, which has a magnitude of several milliamperes, and are collected on screen 18. Tube 37 isemployed to direct the flow of gas and particles along substantially the entire length of screen 18 thereby enhancing dust collection. Tube 37 can be of either a conducting material or a dielectric material.

A large percentage, on the order of about percent, of the dust particles in the gas stream is precipitated in this portion of the apparatus. The gas is moved by fan 7 from precipitator means 14 through filter means 40 of formainous material while an electric field is applied to filter means 40. Inparticular, gas passes outwardly from precipitator 14 through screen 18 and enters the space between screen 18 and filter means 40 where it is subjected to an electrical field between screen 18 and screen 45. The potential difference between screen 45 and screen 18 is typically the same as between corona electrode 24 and screen 18. In this case, conductor 47 shown in FIGS. 1 and 4 is connected to housing 10. The electric field may, however, be either greater or lesser in relative magnitude as a matter of design choice. Filter means 40 serves to remove the remainder of the particulate matter from the gas stream. Clean gas then is withdrawn from filter means 40 by fan 7 and leaves the apparatus through outlet 12. While gas is moved through the apparatus by fan 7 connected to outlet 12 which serves to draw gas through the apparatus in the present illustration, the gas could be moved by a fan in inlet 11 which would force or propel gas through the apparatus.

The presence of filter means 40 of foraminous, dielectric material serves to provide a physical matrix for collection of a filtration cake and to provide a local concentration of the electrostatic field due to the dielectric properties of the filter material. The provision of filter means 40 in this field produces an interaction between the field and the dielectric structure, for example the dielectric fibres in the case of cloth filter material, which tends to intensify the electric field and produce local concentrations which act upon the charged particles which have escaped collection in precipitator means 14. As a result, the present invention provides better dust collection than would be acheived by either precipitator means 14 alone or filter means 40 alone. This is particularly apparent in that it has been found not to be necessary to collect a layer of dust on the filter means 40 to create a filter cake in order to achieve good results. Furthermore, small holes in the material of filter means 40, such as in fabric or cloth material, which would normally cause leaking of dust, have no effect when the filter material is in the electrostatic field according to the present invention. Another important result provided by the method and apparatus of the present invention is that the effect of the electrostatic field on the filter means 40 permits the use of much more porous material for filter means 40 than could be employed heretofore without the problem of bleeding dust through the filter material.

It is important that filter means 40 be located closely adjacent screen 45. In the present illustration filter 40 is in the form of a tube or sleeve and is nearly the same diameter as screen 45 and is not in close proximity to screen 18 or tube 37 of precipitator 14. In other words, the distance from the precipitator 14 to filter means 40 should be greater than the distance between filter means 40 and screen 45. If this relationship is not maintained and filter means 40 were to be positioned near the positive electrical potential of screen 18 or tube 37 the field concentrations produced by filter means 40 can result in a back corona effect with consequent electrical arcing in the space between corona electrode 24 and screen 45.

After the dust collector apparatus is operated for some period of time corona wire 24, screens 18 and 45 and filter means 40 become coated with dust and other particulate matter removed from the gas stream and must be cleaned. This is accomplished according to the present invention by shutting off the flow of gas through the apparatus and shaking the structure in a manner such that the collected dust falls down through the aperture 62 and may then be collected by suitable means such as a hopper for removal from the apparatus. The annular space between the bottom of tube 37 as viewed in FIG. 4 and the top surface of member 22' allows dust removed from the surface of filter means 40 to fall therethrough and into aperture 62. Advantageously, no reverse flow of air is required for the cleaning process and the cleaning may be done while the electrical power for the apparatus remains on. If desired, however, reverse air may be used and the electrical power may be turned off during cleaning but these actions are not necessary for an effective cleaning action. In an installation having a large number of units as in the installation of FIGS. 68, the cleaning operation is performed separately or individually on each of the groups or modules of dust collector units. The cylinder 122 for the particular group of units to be cleaned is operated to lower plate or damper 120 thereby stopping the fiow of gas through only that particular group and then the vibrator 108 for that group is operated to shake all six units of that group simultaneously. When this is completed, cylinder 122 is operated to raise damper 120 thereby placing the group or module in operation again, and if desired the next or adjacent group can be shut off and cleaned in the same manner. As

shown in FIG. 6, removable covers 14) and 142 con- It is therefore apparent that the present invention accomplishes its intended objects. The method and apparatus of the present invention provides a desirable combination of the attributes of dust collection by electrostatic precipitation and the attributes of dust collection by mechanical filtration which utilizes a porous filter medium such as fabric filters or bag houses. I-Ieavy dust loads can be handled with low pressure drops through the apparatus, as in the case of electrostatic precipita tors, and very effecient collection of small dust particles can be achieved with attendant safety from the risk of passage of large puffs of dust as in the case of bag houses. Furthermore, the method and apparatus of the present invention produces results superior to those produced by either electrostatic precipitation or mechanical filtration alone. A typical operation of the apparatus would be at a dust loading of between about ten and about twenty grains per cubic foot, an air/cloth ratio of from about 20 to about 30 in the instance where filter means 40 is of cloth or fabric material, and a pressure drop of about 3 inches of water in the apparatus with an efficiency greater than 99 percent. The combination of electrostatic precipitator means and filter means of foraminous dielectric material having an electrostatic field applied to the filter means produces several desirable effects. Particle collection is very effective due to the electrostatic forces acting in combination with the structure of the filter means, such as the fibers in the case of fabric or cloth. Very porous filter materials can be employed, and holes in the filter material are of minor significance. Filter means 40 serves to catch any momentary passages of dust from the precipitator means 14 due to arcing or similar electrical prob lems. The apparatus of the present invention is readily adaptable to a modular arrangement wherein the individual units can be readily replaced and can be combined into modular sections which, in turn, can be replicated as desired to produce the required capacity in a particular installation. Maintenance of the apparatus is made relatively easily due to the fact that the cartridges or units are adjusted at the top thereof.

While a single embodiment of the present invention has been described in detail, this has been done for the purpose of illustration, not limitation.

We claim:

1. Apparatus for separating particulate matter from a gas stream comprising:

a. a housing having an inlet for receiving dirty gas and an outlet;

b. electrostatic precipitator means within said housing having an inlet communicating with said dirty gas inlet, said precipitator means including collector means for separating a major portion of the particulate matter from the gas stream;

c. filter means comprising a hollow perimetric sheet of foraminous dielectric material within said housing spaced between said electrostatic precipitator and said housing outlet for separating the remainder of the particulate matter from the gas stream;

d. means for applying an electric field to said formaninous filter means comprising a hollow perimetric screen of electrically conducting material positioned between said filter means and said housing outlet and means for applying an electrical potential difference between said screen and said electrostatic precipitator, said screen being located closely adjacent said filter means and the distance from said precipitator to said filter means being greater than the distance between said filter means and said screen; and

e. means for moving gas from said dirty gas inlet through said electrostatic precipitator means and said filter means and to said housing outlet.

2. Apparatus according to claim 1, wherein said electrostatic precipitator is generally cylindrical in shape and of the type wherein gas flows in said precipitator generally axially thereof and flows from said precipitator generally radially outwardly thereof and wherein said filter means is generally tubular in shape and surrounds said precipitator.

3. Apparatus according to claim 1, wherein said filter means is of fabric material.

4. Apparatus according to claim 1, further including vibrator means connected to said precipitator means and said filter means for agitating the same to remove collected particulate matter during cleaning of said apparatus.

5. Apparatus according to claim 1, wherein said electrostatic precipitator comprises a cylindrical collecting structure having an opening at one end defining said inlet and outlet means spaced axially from said inlet, an elongated corona electrode mounted centrally of said collecting structure, and means for applying an electrical potential difference between said corona electrode and said collecting structure.

6. Apparatus according to claim 5, wherein said foraminous filter means comprises a tubular member of fabric material surrounding and positioned in spaced, generally coaxial relation to said collecting structure.

7. Apparatus according to claim 5, wherein said corona electrode is connected to electrical ground and said collecting structure is connected to a relatively positive electrical potential.

8. Apparatus for separating particulate matter from a gas stream comprising:

a. a housing having an inlet for receiving dirty gas and an outlet;

b. electrostatic precipitator means within said housing having an inlet communicating with said dirty gas inlet, said precipitator comprising a cylindrical collecting structure having an opening at one end defining said inlet and outlet means spaced axially from said inlet, an elongated corona electrode mounted centrally of said collecting structure, and means for applying an electrical potential difference between said corona electrode and said collecting structure, said collecting structure comprising a cylindrical screen of electrically conducting material having an operative axial length substantially equal to the operative axial length of said corona electrode and an impervious tube surrounding said screen in closely-spaced relation, said tube extending along a major portion of the axial length of said screen whereby gas is caused to flow along a major portion of the length of said collecting structure prior to flowing through the outlet of said structure;

c. filter means of foraminous material within said housing between said electrostatic precipitator and said housing outlet;

d. means for applying an electric field to said foraminous filter means; and

e. means for moving gas from said dirty gas inlet through said electrostatic precipitator means and said filter means and to said housing outlet.

9. Apparatus according to claim 8, wherein said means for applying an electric field to said foraminous filter means comprises:

a. a cylindrical screen of electrically conducting material surrounding said filter means; and

b. means for applying an electrical potential difference between said screen and said electrostatic precipitator.

10. Apparatus according to claim 9, wherein said screen is located closely adjacent said fabric filter means, the distance from said precipitator to said fabric filter means being greater than the distance between said fabric filter means and said screen.

11. Apparatus for separating particulate matter from a gas stream comprising:

a. a housing having an inlet for receiving dirty gas and an outlet;

b. electrostatic precipitator means within said housing having an inlet communicating with said dirty gas inlet;

0. filter means of forarninous material within said housing between said electrostatic precipitator and said housing outlet;

d. means for applying an electric field to said foraminous filter means comprising a screen of electrically conducting material positioned between said filter means and said housing outlet and means for applying an electrical potential difference between said screen and said electrostatic precipitator;

e. said screen being disposed generally vertically in said housing and supported by said housing and said precipitator means and said filter means being positioned within said screen;

f. means engaging said screen at a position above said precipitator means and said filter means for supporting said precipitator means and said filter means from said screen; and

g. means for moving gas from said dirty gas inlet through said electrostatic precipitator means and said filter means and to said housing outlet.

12. Apparatus according to claim 11, wherein said filter means is of flexible material and wherein said apparatus further comprises:

a. tension applying means connected to said supporting means and to said filter means;

b. means on said filter means engaging said precipitator means in a manner such that tension forces applied to said filter means also are applied to said precipitator means in a direction toward said sup porting means; and

c. spacing means positioned between said precipitator means and said supporting means for limiting movement of said precipitator means toward said supporting means.

13. Apparatus according to claim 1, further including a plurality of units, each unit comprising an assembly of precipitator means, filter means and field applying means, and wherein said housing includes means for arranging said units in groups thereof.

14. Apparatus according to claim 13, further including means for selectively and individually controlling the flow of gas from said groups of units to said housing outlet.

15. Apparatus according to claim 13, further including vibrator means for each group of units, each unit of a group being connected to the corresponding vibrator means, whereby all units of a group are agitated simultaneously to remove collected particulate matter during cleaning of said apparatus.

16. Apparatus for separating particulate matter from a gas stream comprising:

a. a housing having an inlet for receiving dirty gas and an outlet;

b. electrostatic precipitator means within said housing having an inlet communicating with said dirty gas inlet, said precipitator being generally cylindrical in shape and of the type wherein gas flows in said precipitator generally axially thereof and flows from said precipitator generally radially outwardly thereof;

c. filter means of foraminous material within said housing between said electrostatic precipitator and said housing outlet, said filter means being generally tubular in shape and surrounding said precipitator;

(1. said precipitator and said filter means being disposed generally vertically in said housing with said precipitator inlet at the bottom thereof, said housing including a generally horizontal supporting member having an opening therein aligned with said precipitator inlet and in communication with said apparatus inlet, said precipitator further including means defining a channel surrounding said precipitator inlet and deformable solid material in said channel, said horizontal supporting member being provided with a first upstanding connecting member around said opening and extending into said deformable solid material and a second upstanding connecting member spaced horizontally from said first member and engaging said filter means;

e. means for applying an electric field to said foraminous filter means; and

f. means for moving gas from said dirty gas inlet through said electrostatic precipitator means and said filter means and to said housing outlet.

17. Apparatus for separating particulate matter from a gas stream comprising:

a. a housing having an inlet for receiving dirty gas and an outlet;

electrostatic precipitator means within said housing having an inlet communicating with said dirty gas inlet, said precipitator comprising an elongated hollow collecting structure having an opening at one end defining said inlet and outlet means spaced longitudinally from said inlet, an elongated corona electrode mounted generally centrally of said collecting structure, and means for applying an electrical potential difference between said corona electrode and said collecting structure, said collecting structure comprising a hollow screen of electrically conducting material having an operative longitudinal dimension substantially equal to the operative longitudinal dimension of said corona electrode and a gas directing element of hollow, elongated shape and impervious material surrounding said screen in closely-spaced relation, said gas directing element extending along a major portion of the longitudinal dimension of said screen whereby gas is caused to flow along a major portion of the length of said collecting structure prior to flowing through the outlet of said structure;

. filter means of foraminous material within said housing between said electrostatic precipitator and said housing outlet;

means for applying an electric field to said foraminous filter means; and

means for moving gas from said dirty gas inlet through said electrostatic precipitator means and said filter means and to said housing outlet.

18. Apparatus according to claim 17, wherein said means for applying an electric field to said foraminous filter means comprises:

19. Apparatus according to claim 18, wherein said screen is located closely adjacent said filter means, the distance from said precipitator to said filter means being greater than the distance between said filter means and said screen. 

1. APPARATUS OR SEPARATING PARTICULATE MATTER FROM A GAS STREAM COMPRISING: A. A HOUSING HAVING AN INLET FOR RECEIVING DIRTY GAS AN OUTLET, B. ELECTROSTATIC PRECIPITATOR MEANS WITHIN SAID HOUSING HAVING AN INLET COMMUNICATION WITH SAID DIRTY GAS INLET, SAID PRECIPITATOR MEANS INCLUDING COLLECTOR MEANS FOR SEPARATING MAJOR PORTON OF THE PARTICULATE MATTER FROM THE GAS STREAM, C. FILTER MEANS COMPRISING A HOLLOW PERIMETRIC SHEET OF FORAMINUOUS DIELECTRIC MATERIAL WITHIN SAID HOUSING SPACED BETWEEN SAID ELECTROSTATIC PRECIPITATOR AND SAID HOUSING OUTLET FOR SEPARATING THE REMINDER OF THE PARTICULATE MATTER FROM THE GAS STREAM, D. MEANS FOR APPLYING AN ELECTRIC FIELD TO SAID FORMANINUOUS FILTER MEANS COMPRISING A HOLLOW PERIMETER SCREEN OF ELECTRICALLY CONDUCTING MATERIAL POSITIONED BETWEEN SAID FILTER MEANS AND SAID HOUSING OUTLET AND MEANS FOR APPLYING AN ELECTRICAL POTENTIAL DIFFERENCE BETWEEN SAID SCREEN AND SAID ELECTROSTATOIC PRECIPITATOR, SAID SCREEN BEING LOCATED CLOSELY ADJACENT SAID FILTER MEANS AND THE DISTANCE FROM SAID PERCIPITATOR TO SAID FILTER MEANS BEING GREATER THAN THE DISTANCE BETWEEN SAID FILTER MEANS AND SAID SCREEN, AND E. MEANS FOR MOVING GAS FROM SAID DIRTY GAS INLET THROUGH SAID LECTROSTATIC PRECIPITATOR MEANS AND SAID FILTER MEANS AND TO SAID HOUSING OUTLET.
 2. Apparatus according to claim 1, wherein said electrostatic precipitator is generally cylindrical in shape and of the type wherein gas flows in said precipitator generally axially thereof and flows from said precipitator generally radially outwardly thereof and wherein said filter means is generally tubular in shape and surrounds said precipitator.
 3. Apparatus according to claim 1, wherein said filter means is of fabric material.
 4. Apparatus according to claim 1, further including vibrator means connected to said precipitator means and said filter means for agitating the same to remove collected particulate matter during cleaning of said apparatus.
 5. Apparatus according to claim 1, wherein said electrostatic precipitator comprises a cylindrical collecting structure having an opening at one end defining said inlet and outlet means spaced axially from said inlet, an elongated corona electrode mounted centrally of said collecting structure, and means for applying an electrical potential difference between said corona electrode and said collecting structure.
 6. Apparatus according to claim 5, wherein said foraminous filter means comprises a tubular member of fabric material surrounding and positioned in spaced, generally coaxial relation to said collecting structure.
 7. Apparatus according to claim 5, wherein said corona electrode is connected to electrical ground and said collecting structure is connected to a relatively positive electrical potential.
 8. Apparatus for separating particulate matter from a gas stream comprising: a. a housing having an inlet for receiving dirty gas and an outlet; b. electrostatic precipitator means within said housing having an inlet communicating with said dirty gas inlet, said precipitator comprising a cylindrical collecting structure having an opening at one end defining said inlet and outlet means spaced axially from said inlet, an elongated corona electrode mounted centrally of said collecting structure, and means for applying an electrical potential difference between said corona electrode and said collecting structure, said collecting structure comprising a cylindrical screen of electrically conducting material having an operative axial length substantially equal to the operative axial length of said corona electrode and an impervious tube surrounding said screen in closely-spaced relation, said tube extending along a major portion of the axial length of said screen whereby gas is caused to flow along a major portion of the length of said collecting structure prior to flowing through the outlet of said structure; c. filter means of foraminous material within said housing between said electrostatic precipitator and said housing outlet; d. means for applying an electric field to said foraminous filter means; and e. means for moving gas from said dirty gas inlet through said electrostatic precipitator means and said filter means and to said housing outlet.
 9. Apparatus according to claim 8, wherein said means for applying an electric field to said foraminous filter means comprises: a. a cylindrical screen of electrically conducting material surrounding said filter means; and b. means for applying an electrical potential difference between said screen and said electrostatic precipitator.
 10. Apparatus according to claim 9, wherein said screen is located closely adjacent said fabric filter means, the distance from said precipitator to said fabric filter means being greater than the distance between said fabric filter means and said screen.
 11. Apparatus for separating particulate matter from a gas stream comprising: a. a housing having an inlet for receiving dirty gas and an outlet; b. electrostatic precipitator means within said housing having an inlet communicating with said dirty gas inlet; c. filter means of foraminous material within said housing between said electrostatic precipitator and said housing outlet; d. means for applying an electric field to said foraminous filter means comprising a screen of electrically conducting material positioned between said filter means and said housing outlet and means for applying an electrical potential difference between said screen and said electrostatic precipitator; e. said screen being disposed generally vertically in said housing and supported by said housing and said precipitator means and said filter means being positioned within said screen; f. means engaging said screen at a position above said precipitator means and said filter means for supporting said precipitator means and said filter means from said screen; and g. means for moving gas from said dirty gas inlet through said electrostatic precipitator means and said filter means and to said housing outlet.
 12. Apparatus according to claim 11, wherein said filter means is of flexible material and wherein said apparatus further comprises: a. tension applying means connected to said supporting means and to said filter means; b. means on said filter means engaging said precipitator means in a manner such that tension forces applied to said filter means also are applied to said precipitator means in a direction toward said supporting means; and c. spacing means positioned between said precipitator means and said supporting means for limiting movement of said precipitator means toward said supporting means.
 13. Apparatus according to claim 1, further including a plurality of units, each unit comprising an assembly of precipitator means, filter means and field applying means, and wherein said housing includes means for arranging said units in groups thereof.
 14. Apparatus according to claim 13, further including means for selectively and individually controlling the flow of gas from said groups of units to said housing outlet.
 15. Apparatus according to claim 13, further including vibrator means for each group of units, each unit of a group being connected to the corresponding vibrator means, whereby all units of a group are agitated simultaneously to remove collected particulate matter during cleaning of said apparatus.
 16. Apparatus for separating particulate matter from a gas stream comprising: a. a housing having an inlet for receiving dirty gas and an outlet; b. electrostatic precipitator means within said housing having an inlet communicating with said dirty gas inlet, said precipitator being generally cylindrical in shape and of the type wherein gas flows in said precipitator generally axially thereof and flows from said precipitator generally radially outwardly thereof; c. filter means of foraminous material within said housing between said electrostatic precipitator and said housing outlet, said filter means being generally tubular in shape and surrounding said precipitator; d. said precipitator and said filter means being disposed generally vertically in saiD housing with said precipitator inlet at the bottom thereof, said housing including a generally horizontal supporting member having an opening therein aligned with said precipitator inlet and in communication with said apparatus inlet, said precipitator further including means defining a channel surrounding said precipitator inlet and deformable solid material in said channel, said horizontal supporting member being provided with a first upstanding connecting member around said opening and extending into said deformable solid material and a second upstanding connecting member spaced horizontally from said first member and engaging said filter means; e. means for applying an electric field to said foraminous filter means; and f. means for moving gas from said dirty gas inlet through said electrostatic precipitator means and said filter means and to said housing outlet.
 17. Apparatus for separating particulate matter from a gas stream comprising: a. a housing having an inlet for receiving dirty gas and an outlet; b. electrostatic precipitator means within said housing having an inlet communicating with said dirty gas inlet, said precipitator comprising an elongated hollow collecting structure having an opening at one end defining said inlet and outlet means spaced longitudinally from said inlet, an elongated corona electrode mounted generally centrally of said collecting structure, and means for applying an electrical potential difference between said corona electrode and said collecting structure, said collecting structure comprising a hollow screen of electrically conducting material having an operative longitudinal dimension substantially equal to the operative longitudinal dimension of said corona electrode and a gas directing element of hollow, elongated shape and impervious material surrounding said screen in closely-spaced relation, said gas directing element extending along a major portion of the longitudinal dimension of said screen whereby gas is caused to flow along a major portion of the length of said collecting structure prior to flowing through the outlet of said structure; c. filter means of foraminous material within said housing between said electrostatic precipitator and said housing outlet; d. means for applying an electric field to said foraminous filter means; and e. means for moving gas from said dirty gas inlet through said electrostatic precipitator means and said filter means and to said housing outlet.
 18. Apparatus according to claim 17, wherein said means for applying an electric field to said foraminous filter means comprises: a. a screen of electrically conducting material positioned between said filter means and said housing outlet; and b. means for applying an electrical potential difference between said screen and said electrostatic precipitator.
 19. Apparatus according to claim 18, wherein said screen is located closely adjacent said filter means, the distance from said precipitator to said filter means being greater than the distance between said filter means and said screen. 